In the production process of a semiconductor wafer of silicon, gallium, arsenic, etc., it is general to carry out a back grinding step of grinding a semiconductor wafer having formed thereon a pattern to a definite thickness. In this case, it is a general method that after adhering a pressure-sensitive adhesive sheet, which becomes a semiconductor wafer-protective sheet, to the surface of the semiconductor wafer for the purpose of protecting the semiconductor wafer, etc., the semiconductor wafer is ground. The semiconductor-protecting pressure-sensitive adhesive sheet is released from the ground semiconductor wafer, and after dicing the semiconductor wafer into small element pieces (IC chips) , they are transferred to a mounting step which is the subsequent step. In this case, the semiconductor wafer is, in the state of previously being adhered with each pressure-sensitive adhesive sheet, transferred to a bonding step which is the subsequent step through the steps of dicing, washing, drying, expanding, and picking up.
In the pressure-sensitive adhesive sheets used in the steps from the grinding step to the picking up step through the dicing step, it is desired as the above-described semiconductor-protecting pressure-sensitive adhesive sheet that the pressure-sensitive adhesive sheet has a sufficient adhesive force to a semiconductor wafer chip from adhering of the pressure-sensitive adhesive sheet to the completion of grinding and also has an adhesive force of the extent that the pressure-sensitive adhesive does no adhere to the semiconductor wafer chip at releasing the semiconductor-protecting pressure-sensitive adhesive sheet before the dicing step after the grinding step. Also, it is desired as the above-described semiconductor wafer-fixing sheet that the pressure-sensitive adhesive sheet has a sufficient adhesive force to a wafer chip from the dicing step to the drying step and also has an adhesive force of the extent that the pressure-sensitive adhesive does not adhere to the wafer chip at picking up.
As such a pressure-sensitive adhesive sheet, JP-A-60-196956 and JP-A-60-223139 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") propose pressure-sensitive adhesive sheets prepared by coating a pressure-sensitive adhesive comprising a low molecular weight compound having at least two photopolymerizable carbon-carbon double bonds in the molecule, capable of forming three-dimensional network by the irradiation of light on the surface of a substrate. Those proposals are pressure-sensitive adhesive tapes each prepared by coating an ultraviolet-curing pressure-sensitive adhesive on a ultraviolet-transmitting substrate, and are based on the principle that the ultraviolet-curable compound contained in the pressure-sensitive adhesive is cured by ultraviolet rays to impart a three dimensional structure to the pressure-sensitive adhesive, thereby greatly lowering the fluidity thereof. As such a pressure-sensitive adhesive, a pressure-sensitive adhesive wherein sufficient curing is obtained by less illumination and exposure amount is desirable from the points of the speed up of the steps and energy saving. However, when the curing reaction proceeds by less illumination and exposure amount, there are problems that the pressure-sensitive adhesive is cured by a slight amount of ultraviolet rays from the surrounding environment of a fluorescent lamp, etc., at the standby for adhering to a wafer, and thus the pressure-sensitive adhesive cannot adhere to the wafer when adhering the same to the wafer before grinding and dicing, and also the pressure-sensitive adhesive does not show a sufficient adhesive force at adhering to a wafer, causing the problems of releasing or slipping the pressure-sensitive adhesive sheet at grinding, which results in making grinding impossible or causing scattering of chips at dicing.
In more detail, in the above-described semiconductor-protecting pressure-sensitive adhesive sheet and the semiconductor wafer-fixing sheet, after coating the ultraviolet-curing adhesive on at least one surface of a substrate film followed by drying, the surface of the coated pressure-sensitive adhesive layer is generally protected with a film called a separator. As the separator film, considering the surface smoothness, the releasing property, etc., a plastic film such as a polyethylene film, a polypropylene film, a polyester film subjected to a releasing agent treatment, etc., is used.
The product form of the pressure-sensitive adhesive film protected with the separator is usually supplied in the form of being wound in a roll form such that the film is continuously adhered to the semiconductor wafers by an automatic adhering apparatus, etc. Also, at forwarding the product, the product is packed with a light-shielding bag, etc., and is protected so that the pressure-sensitive adhesive is not cured by the exposure of ultraviolet rays from a surrounding environment such as sun light, illumination, etc. At the adhering work by an automatic adhering apparatus, the sheet roll is mounted to a definite position of the apparatus. However, the automatic adhering apparatus itself does not have a function of protecting from the exposure of ultraviolet rays, etc., and thus during using the automatic adhering apparatus, it is always exposed to ultraviolet rays from the surrounding environment. The exposure to a fine amount of ultraviolet rays from the surrounding environment does not give a serious problem in the case of a conventional ultraviolet-curing pressure-sensitive adhesive having a weak reactivity to a fine exposure of ultraviolet rays. However, in the case of the ultraviolet-curing pressure-sensitive adhesive sufficiently curing with a small amount of ultraviolet rays, which has been required at present, the curing reaction proceeds even by the exposure of a fine amount of ultraviolet rays, whereby the problems of the occurrences of inferior grinding at grinding and scattering of chips at dicing, an inferior pick up at picking up, etc., are sometimes caused.